US2713912A

US2713912A - Wall scratcher apparatus

Info

Publication number: US2713912A
Application number: US27299A
Authority: US
Inventors: Reuben C Baker
Original assignee: Baker Oil Tools Inc
Current assignee: Baker Hughes Oilfield Operations LLC
Priority date: 1948-05-15
Filing date: 1948-05-15
Publication date: 1955-07-26
Anticipated expiration: 1972-07-26

Description

July 26, 1955 R C BAKER 2,713,912

WALL SCRATCHER APPARATUS Filed May 15, 1948 2 Sheets-Sheet 1 25 C gum 35 i mil 25 guii IMM; .ff Q@ mine f 4j \\z 2 1 l a MII I 26 l f 1 "l" 27 mu "n *f8 dug@ "a 5 l5 6, 23 76 33 25 .g 5 winnt '25,4 a 9 im" 25 f2 52 llllllll F l l ff l ff i I m i 6 JNVENTOR.

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Arroz/vars United States Patent WALL SCRATCHER APPARATUS Reuben C. Baker, Coalinga, Calif., assignor to Baker Oil lools, Inc., Los Angeles, Calif., a corporation of Caliorma Application May 15, 1948, Serial No. 27,299

17 Claims. (Cl. 166-173) The present invention relates to apparatus for removing mud sheaths or cakes from the walls of well bores.

In the rotary drilling of well bores, mud is circulated down the drill pipe for outward passage through the drill bit and upward movement through the annulus around the drill pipe to the top of the well bore. The drilling mud forms a mud sheath or cake on the wall of the hole, which oftentimes interferes with the subsequent proper cementing of a casing or liner string, or similar conduit, in the well bore. It has been found that the mud cake may prevent proper bonding ofthe cement to the hole wall, and may invite channeling of the cement slurry during upward passage of the latter around the conduit string. Channeling, as well as a non-uniform distribution of cement around the conduit string, may also be caused by a non-coaxial disposition of the conduit string in the well bore.

It has been proposed, heretofore, to remove the mud cake from the Wall of the well bore in the region where a proper cement bond is required by means of wall scratchers mounted on the casing or conduit string. These scratchers usually include a plurality of spring-like wire projections, which scratch the mud from the desired region of the formation wall upon movement of the casing string. During their downward travel with the conduit string while running the latter in the hole, the projections ride the formation wall and wear their outer scratching portions unduly. In some cases, the wear may be suciently extensive to render the projections ineffective for scratching the wall properly at the desired region in the hole. In addition to subjecting the projections to undue wear, they remove the mud sheath at undesired regions in the well bore during running of the conduit string therein. Such removal is undesirable in view of theuse of the drilling mud to prevent blowouts.

It is, accordingly, an object of the present invention to improve wall scratchers of the type above indicated.

Another object of the invention is to minimize, if not eliminate entirely, the wear on the projecting elements of the scratcher as it is lowered in the well bore.

Another object of the invention is to provide a wall scratcher, which avoids removal of the mud sheath during lowering of the casing or conduit string in the well bore, until the casing string is manipulated appropriately at the region where the removal of the mud sheath is desired.

A further object of the invention is to provide a wall scratcher apparatus which is effective to center the casing in the well bore, in addition to its normal function of removing the mud sheath or cake.

Still another object of the invention is to insure the outward projection of the scratcher elements into the wall of the hole during movement of the casing string, preferably in an upward direction.

Yet a further object of the invention is to move the scratcher elements positively against the formation wall during movement of the casing string in the desired di- Section, which is preferably upwardly.

' secure the rubber mounting member thereto.

`ice

Another object of the invention is to obtain ushing of the mud scratchings and formation material from the scratcher elements and from the region being scratched.

Still a further object of the invention is to provide a wall scratcher which is of strong and sturdy construction, and capable of being manufactured economically.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of several forms in which it may be embodied. Such forms are shown in the drawings accompanying and forming part of the present specication. These forms will now be described in detail, illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure l is a side elevation of one form of wall scratcher' mounted upon a casing disposed in a well bore;

Fig. 2 is an enlarged, longitudinal fragmentary section of the wall scratcher disclosed in Fig. 1 with parts broken away;

Fig. 3 is a view, similar to Fig. 2, of another form of wall scratcher embodying the invention;

Fig. 4 is a longitudinal view, partly in section and partly in elevation, of still another form of the invention disposed in a well bore, with the parts in relatively retracted position;

Fig. 5 is a sectional and longitudinal view similar to Fig. 4, disclosing the scratcher projections in their outermost position;

Fig. 6 is a longitudinal view, partly in section and partly in elevation, of still another form of theinvention, with the projecting elements in relatively retracted position;

Fig. 7 is a view similar to Fig. 6, disclosing the pro-k jecting elements in fully extended position;

Fig. 8 is a partial sectional View, on an enlarged scale, with parts broken away, of part of the apparatus disclosed in Fig. 6; and

Fig. 9 is a view similar to Fig. 8, disclosing a portion of the scratcher apparatus, with the parts in the position shown in Fig. 7.

The wall scratcher A disclosed in Figs. l and 2 is mounted upon a section 10 of a casing, liner, or other conduit string, for movement therewith through a well4 bore during lowering of the conduit string to a predetermined position. It is desired to scratch the mud sheath or cake from a region of the well bore. To achieve this purpose, a plurality of scratcher teeth 11 are disposedin spaced relation substantially uniformly around the casing section 10, being carried within an annular mounting member 12 of rubber, or other suitable flexible or elastic material, surrounding the casing. As specifically shown in the drawings, the scratcher teeth 11 may consist of wire projections or nails, whose pointed ends 13 face outwardly, and whose inner shank portions 14 are molded into the rubber body or mounting member 12. The wire projections 11 are molded in the rubber member,

so that they are normally inclined outwardly and in an upward direction, as clearly shown in Figs. l and `2.

'For the purpose of insuring against pulling of each wire projection from the rubber mounting member 12, the latter is contained within a ring or sleeve 15, having upper and lower end anges 16, which preferably converge in an outward direction toward eachother, to The sleeve is also provided with an intermediate rib or bead 17 having longitudinally extending slots 18 therein, through which the wire projections 13 extend. The heads 19 of the wire projections orvnails are disposed within the,- inner groove or recess 20 formed by the bead 17, with the heads 151 engaging the inner surface of the bead defining the slots 18.

When the wire projections or teeth 11 are disposed in their-normal position facing upwardly and outwardly, their head ends are at the upper portions of the slots 18. The projections, however, can be moved downwardly to extend their points 13 further outwardly against the spring, or resisting, force of the rubber body member 12. During such movement, the inner portions of the scratcher elements 11 move downwardly within the slots 1S, their outward movement being prevented by engagement of the heads 19 with the inner surface of the bead 17.

The wire scratcher A may be mounted upon a casing or other conduit section 10, being confined against substantial longitudinal movement by upper and

lower stop rings

21, 22 suitably secured to the casing section, as by use of one or more headless screws 23 passing through the rings and bearing against the casing section.

The casing section forms part of the casing string, which is then lowered in the well bore. During such lowering movement, the upper stop ring 21 engages the ring or sleeve 1S, and forces the rubber mounting member 12 and the teeth 11 downwardly along the wall of the well bore. When moving downwardly, the wire scratcher elements or teeth contact the wall of the hole comparatively lightly, in view of their upwardly inclined arrangement. As a matter of fact, any tendency for the teeth to dig into the wall to any substantial extent causes them to swing upwardly and inwardly to a further extent against the resisting force of the rubber body member 12. Inward movement of the teeth to any substantial extent will be prevented by engagement of the heads 19 with the casing section 10.

When the region in the well bore is reached at which the mud sheath or cake is to be scratched or removed from the formation wall, the entire casing string B is moved upwardly, effecting upward movement of the scratcher A, because of engagement of the lower stop ring 22 with the sleeve 15. Since the tooth points 13 are engaged with, and may actually penetrate, the mud sheath C to a slight extent, such upward movement tends to shift the tooth points 13 further outwardly toward a position in which the projections 11 are substantially at right angles to the scratcher and casing axis (Fig. 2). In this position, the outer portions 13 of the teeth penetrate the mud sheath C and may also extend into the formation wall itself, depending upon the length of the teeth. The casing string is elevated the desired distance, which may be 30 ft., as an example, and in so doing, the scratcher teeth 11 will scrape or scratch the mud sheath, and also some formation material, from the wall of the well bore. The casing may be reeiprocated the desired number of times until the entire mud sheath has been removed from the formation wall along the required length. As noted above, downward movement of the casing string B will have very little effect upon the mud sheath, whereas upward movement will cause penetration of the teeth 11 through the mud sheath C and into the formation wall, to cut the sheath from the latter.

The rubber body member 12 serves to mount or hold the wire projections 11 in appropriate relation with respect to one another. In addition, it provides a springlike force tending to shift the teeth upwardly to their initial inclined positions, which positions will be assumed upon movement of the casing string in one direction, such as downwardly. Movement of the casing string in the opposite direction, such as upwardly, causes the penetrating action of the tooth points 13, as described above, and their effective removal of the mud sheath C.

The rubber mounting member 12 has still a further desirable function, which is to effect flushing of the mud and formation scratchings from the teeth 11, and maintain them in clean condition for most eicient penetration into the mud sheath and formation wall. It is to be noted that the area of the annulus D between the periphery of the rubber body member 12 and the formation wall or mud sheath is substantially less than the annular area E between the periphery of the casing 10 and mud sheath or formation wall. As a result, during longitudinal movement of the casing string B in the well bore, the lluid is being displaced and must accelerate or increase in velocity in passing through the lesser annular area D around the body member 12. This increase in velocity of the fluid causes it to clean the teeth 11 of scratchings.

As an example, movement of the casing string upwardly will cause the fluid in the well bore to move relatively in a downward direction and will eect cleaning of the scratcher teeth. Similarly, movement of the casing string in a downward direction will cause the well tiuid to move relatively upward and increase in velocity through the narrower annular space D, also cleaning the scratcher teeth.

In the embodiment of the invention disclosed in Figs. l and 2, the projecting teeth 11 have been molded to the rubber body member 12, and have also been disposed through the slotted sleeve 15. In the form of invention disclosed in Fig. 3, the tooth members or wire nails 11 have been molded into an annular rubber body member 12a, which is vulcanized to a mounting ring or sleeve 15a adapted to t the casing 10. The heads 19 of the teeth are also molded in the rubber body member 12a, and in view of their much greater diameter than the shank por tions 14 of each tooth will resist removal of the teeth 11 from the rubber body member.

The scratcher device disclosed in Fig. 3 is mounted on the casing section 10 between the upper and lower stop rings 21, 22, in the same manner as the embodiment illustrated in Figs. l and 2, and is used and manipulated in the same fashion to effect removal of the mud sheath C from the formation wall.

In the form of invention illustrated in Figs. 4 and 5, a wall scratcher apparatus is disclosed which does not rely upon initial engagement or penetration of the teeth 11 with the mud sheath C or formation wall in expanding the points 13 outwardly. The outward expansion is positive.

Thus, the wall scratcher device F is essentially the same as the form disclosed in Fig. 2, although the form disclosed in Fig. 3 could be used in its place. The scratcher device is mounted on the casing section 25 adjacent and immediately above a coupling collar 26 connecting the upper section to a lower casing section 27. This collar 26 forms a lower stop for the wall scratcher device F. Disposed above the wall scratcher is an actuating member in the form of a cup-shape actuating ring 2S, having a ange 29 slidable along the upper casing section 25, and a depending skirt 30 spaced outwardly from the casing section and engageable with the projecting teeth 11.

Above the actuating member 28 is a friction drag device G, which may also function as a casing centralizer. One of its purposes is to cause downward movement of the actuating ring 28 upon upward movement of the casing string B, in order that the ring will bear downwardly upon the projecting teeth 11 and shift them outwardly through the mud sheath C, and possibly into the formation wall.

T he casing centralizer and friction drag device G may assume any suitable form. As disclosed in the drawings. and particularly Figs. 6 and 7, it includes upper and lower longitudinally spaced

collars

31, 32, to which a plurality of circularly spaced outwardly bowed drag springs 33 are secured, as by welding. These collars 31. 32 are slidable on the casing section 25, their movement with respect thereto being limited by stop elements, in the form of upper lugs 34 disposed below and adjacent the upper collar 31, and by lower lugs 35 disposed immediately above and adjacent the lower corlar 32. These atlanta,

lugs are suitably secured, as by Welding, to the casing section 25. i

The outwardly bowed springs 33 frictionally engage the wall of the well bore or mud sheath, which tends to resist longitudinal movement of the drag device G with the casing string B. During downward movement of the apparatus in the well bore, the drag device G tends to move relatively upward on the casing section, such movement being limited by engagement of the lower collar 32 with the lower stop lugs 35. The lower collar 32 thereupon operates as a stop member, limiting upward movement of the actuating ring 28, which, in turn, prevents substantial upward movement of the wall scratcher F away from the stop shoulder 36 formed by the coupling member 26.

During downward movement of the casing string B, the scratcher elements 11 are inclined in an upward and outward direction, and will have very little, if any, scratching action upon the mud sheath (Fig. 4). When the region in the well bore is reached at which the mud sheath is to be removed, the casing string B is moved upwardly. During such upward movement, the shoulder 36 engages the wall scratcher F and moves it upwardly with the casing string. At the beginning of such upward movement, the drag device G does not move upwardly because of the frictional engagement of the bowed springs 33 with the formation wall. As a result, the teeth 11 are forced against the lower end of the actuating ring skirt 30, which projects the teeth outwardly into the mud sheath C, and possibly into the formation wall, into the position disclosed in Fig. 5. Upward movement of the casing string to the desired extent will cause the tooth projections 13 to scratch the mud sheath from the formation wall.

At the initial portion of the upward movement of the casing string B, and after the projections 11 have been expanded outwardly to their fullest extent, the upper lugs 34 will engage the upper collar 31 and exert a pulling action on the drag device G upwardly along the formation wall.

The apparatus may be moved up and down with the casing string the desired number of times, to insure full removal of the mud sheath from the formation wall. During upward movement, the actuating ring 30 forces all of the projecting elements 11 outwardly into the mud sheath C. During downward movement, the rubber body member 12 will partially retract all of the teeth 11 to their initial upwardly inclined position, since the drag device G moves away from the actuating ring 30.

In addition to its positive actuation of the wall scratcher elements 11, the drag device G serves to center the casingl string in the well bore. Such centering insures substantially equal penetration of all of the scratcher elements into the mud sheath and guards against unduly overloading any of them, which might otherwise occur should the casing lean against one side of the formation wall. The centering action also insures the deposition of a uniform body of cement around the casing string as a result of subsequent cementing operation. A plurality of wall scratchers maybe mounted upon the casing string and be positively actuated in electing removal of the mud sheath from the formation wall. As disclosed in Figs. 6 to 9, inclusive, several wall scratchers H, J, K are slidably mounted on the casing string B, with the lowermost scratcher K adapted to engage a suitable stop member, such as the casing coupling collar 26. The wall scratchers are separated by cup-shaped actuating rings 28a, 28b, 28C. The flange portions 29 of all but the uppermost ring 28a engage the adjacent upper scratcher body 12a and sleeve 15a. The uppermost actuating member 28a is engageable with the lower collar 32 of the drag device G, in the same manner as described in connection with the apparatus shown in Figs. and 4. The wall scratchers disclosed are of the type illustrated in Fig. 3, although they could be the same as illustrated in Figs. 1, 2, 4 and 5, if desired.

During downward movement of the casing string n the well bore, the teeth 13 of the wall scratchers H, J, K, occupy their upwardly directed inclined position (Figs. 6 and 8). When the region in the well bore is reached at which the scratching operation is to take place, the casing string B is moved upwardly, which causes the collar 26 to engage the lowermost wall scratcher K and shift all of the scratchers H, I, K and intervening actuating members 28a, 28b, 28e against one another, with the uppermost actuating member being disposed against the lower collar 32 of the drag device and casing centralizer G. Continued upward movement of the casing string to a slight extent will cause the teeth 11 of the uppermost scratcher H to be projected outwardly by the upper actuating member 28rz, the intermediate actuating member 28b engaging the teeth of the intermediate scratcher I, and projecting them outwardly, and the lowermost teeth being engaged and projecting outwardly by the lowermost actuating member 28C. In general, the teeth will occupy the general positions illustrated in Figs. 7 and 9.

The casing string is moved upwardly to the desired extent to scratch the mud sheath C from the formation wall, and may be moved up and down a sucient number of times until the formation wall is free of the mud sheath. During such upward and downward movement, the iluid in the well is caused to increase its Velocity in moving through the narrow annular space D between the `actuating rings 28a, 2Sb, 28C and the formation wall,

which cleans the projecting teeth 11 of mud and formation scratchings, in the same manner as described above in connection with the other forms of the invention. This is also true of the apparatus disclosed in Figs. 4 and 5.

In view of the positive actuation of the teeth on the scratchers disclosed in Figs. 4 to 9, inclusive, it is unnecessary for their outer points 13 to engage the mud sheath or formation wall during downward travel of the casing string B in the well bore to the desired region at which the mud sheath is to be removed. Thus, the initial upwardly inclined position of the teeth may be such that the points 13 are free from engagement with the formation wall, the casing centralizer G maintaining the teeth uniformly spaced and out of engagement with the latter. Because of this arrangement, none of the mud cake or sheath is removed during running of the casing string in the well bore. However, when the mud sheath is to be removed at any desired region, upward movement of the casing string B will cause the drag device G to eifect positive and forcible shifting of the tooth projections 11 f outwardly into the mud sheath C, thereby obtaining removal of the latter from the formation wall, in the man ner described above.

By virtue of the avoidance of dragging of the teeth 11 on the mud sheath or formation wall during lowering of the casing string in the well bore, assurance is had that the points 13 will be sharp and capable of penetrating the mud sheath when its removal is desired. Assurance is further had against damage to the wall scratcher or scratches during lowering of the casing string in the well bore. Of course, if desired, the teeth can be made long enough so as to engage the mud sheath or formation wall during the entire lowering of the casing string in the bore hole.

The inventor claims:

l. In a wall scratcher: a resilient rubber body member; a sleeve on which said member is mounted; and a plurality of scratcher elements extending through said body member and sleeve and projecting outwardly in radial planes from said body member.

2. In a wall scratcher: a sleeve having a plurality of circumferentially spaced holes therein; a resilient rubber body member mounted on said sleeve; and a plurality of scratching elements extending through said holes and body member and projecting outwardly in radial planes from said body member.

3. In a wall scratcher: a sleeve having a plurality of circumerentially spaced slots therein extending longitudinally of the axis of the sleeve; a resilient rubber body member mounted on said sleeve; and a plurality of scratching elements extending through said slots and body member and projecting outwardly in radial planes from said body member, said scratching elements having stop portions engageable with the inside of said sleeve.

4. In a wall scratcher: a metal sleeve; a resilient rubber body member mounted on said sleeve; said sleeve having a medial rib provided with circumferentially spaced holes; and a plurality of wire scratching elements extending through said holes and body member and projecting outwardly in radial planes from said body member, said scratching elements having stop portions disposed within and engageable with said rib.

5. In a wall scratcher: a resilient, circumferentially continuous, annular rubber body member; a cylindrical sleeve on which said member is mounted; and a plurality of scratcher elements individually embedded and molded directly in said body member and projecting outwardly therefrom in radial planes to a substantial distance in a direction inclined upwardly and outwardly to the axis of said body member and sleeve.

6. In a wall scratcher: a resilient, circumferentially continuous, annular rubber body member; a metallic cylindrical sleeve member on which said rubber member is mounted; a plurality of scratcher elements embedded and molded directly in said body member and projecting outwardly and upwardly therefrom to a substantial extent; and stop portions on said elements disposed in one of said members.

7. In a wall scratcher: a circumferentially continuous rubber annular body member; and a plurality of individual scratcher elements embedded and molded directly in said body member in circumferentially spaced adjacent relation to each other and 'free from connection to each other both axially and circumerentially and projecting outwardly from said body member to a substantial distance in a direction inclined to the axis of said body member, said elements lying in planes radial of the member axis.

8. In a wall scratcher: a circumferentially continuous rubber annular body member; and a plurality of individual wire elements embedded and molded directly in said body member in circumferential spaced adjacent relation to each other and free from connection to each other both axially and circumferentially and extending outwardly from said body member a substantial distance in a direction inclined to the axis of said member, said elements lying in planes radial of the member axis.

9. In apparatus of the character described: a wall scratcher adapted to be mounted on a running-in string positionabie in a well bore, said scratcher having circumferentially spaced outwardly extending Wire scratcher elements disposed around the running-in string and being supported at their inner portions only to provide a large number of free scratching ends adapted to engage and scratch the wall of the well bore; and means adapted to be mounted on said running-in string and movable longitudinally with respect to the running-in string in response to manipulation of said string for projecting said elements radially outward.

l0. ln apparatus of the character described: a wall scratcher adapted to be mounted on a tubular string positionable in a well bore, said scratcher having circumferentially spaced outwardly extending wire scratcher elements disposed around the tubular string and providing a large number of free scratching ends adapted to engage and scratch the wall of the Well bore; and means adapted to be mounted on said tubular string and engageable with said elements to project said elements radially outward, said means including a drag device Cil engageable with the wall of the well bore and adapted to be mounted on the tubular string.

ll. In apparatus of the characterdescribed: a wall scratcher adapted to be mounted on a casing string positionable in a well bore, said scratcher having circumferentially spaced outwardly extending wire scratcher elements disposed around the casing string and providing a large number of free scratching ends adapted to engage and scratch the wall of the well bore; and means adapted to be mounted on said casing string and engageable with said elements to project said elements radially outward, said means including a casing centralizer adapted to be mounted on the casing string.

l2. In apparatus of the character described: a runningin string having alternately arranged wall scratchers and actuating members mounted thereon, said scratchers including circumferentially spaced outwardly extending wire scratcher elements disposed around the running-in string and providing a large number of free scratching ends adapted to engage and scratch the wall of the well bore, and said actuating members being adapted to engage said elements for projecting them radially outward; and means on and carried by said running-in string movable longitudinally with respect to and along the exterior of said running-in string in response to manipulation of said string for causing said actuating members to project said elements outwardly.

13. In apparatus of the character described: a casing having alternately arranged wall scratchers and actuating members mounted thereon, said scratchers including circumterentially spaced outwardly extending wire scratcher elements disposed around the casing and providing a large number of free scratching ends adapted to engage and scratch the wall of a well bore, and said actuating membcrs being adapted to engage said elements for projecting them radially outward; and means mounted on said casing for causing said actuating members to project said elements outwardly, said means including a drag device on said casing engageable with the wall of the well bore in which said casing is disposed.

14. In apparatus of the character described: a casing string having alternately arranged wall scratchers and actuating members mounted thereon, said scratchers including circumferentially spaced outwardly extending wire scratcher elements disposed around the casing string and providing a large number of free scratching ends adapted to engage and scratch the wall of a well bore in which said casing string is disposed, and said actuating member being adapted to engage said elements for projecting them radially outward; and a casing centralizer mounted on said casing string and engageable with one of said actuating members for causing all of said actuating members to project said elements outwardly.

l5. In apparatus of the character described: a wall seratcher adapted to be mounted on a running-in string positionable in a well bore and having circumferentially spaced outwardly extending wire scratcher elements disposed around the running-in string and being supported at their inner portions only to provide a large number of free scratching ends adapted to engage and scratch the wall of the well bore; and means adapted to be mounted on the running-in string and engageable with said elements and movable longitudinally of the axis of the scratcher for projecting said elements laterally outward.

16. In apparatus of the character described: a wall scratcher adapted to be mounted on a tubular string positionable in a well bore, said scratcher having circumferentially spaced outwardly extending wire scratcher elements disposed normally in an upward and outwardly inclined position, said elements also being disposed around the tubular string and being supported at their inner portions only to provide a large number of free scratching ends adapted to engage and scratch the wall of the Well bore; and means mounted on said tubular string and movable downwardly into engagement with said elements to project said elements radially outward, said means including a drag device mounted on the tubular string and engageable with the wall of the Well bore.

17. 1n apparatus of the character described: a wall scratcber adapted to be mounted on a casing string pos.- tionable in a well bore, said scratcher having circumferentially spaced outwardly extending wire scratcher elements disposed normally in an upward and outwardly inclined position, said elements also being disposed around the casing string and being supported at their inner portions only to provide a large number of free scratching ends adapted to engage and scratch the wall of the well bore; and means adapted to be mounted on said casing string and engageable with said elements to project said elements radially outward upon downward movement of said means relative to said casing string, said means including a casing centralizer adapted to be mounted on said casing string.

References Cited in the tile of this patent UNTED STATES PATENTS